Meaning of the Words Compass and Protractor
Date: 08/17/99 at 22:45:01 From: Heather Bugbee Subject: Compasses and protractors Dear Dr. Math, Why is a compass called a compass when it protracts and retracts, and why is a protractor called a protractor when it is used to measure degrees? I know this is not really a high school math question, but it intrigues me a great deal. Thank you for your time. Heather Bugbee
Date: 08/18/99 at 13:13:31 From: Doctor Peterson Subject: Re: Compasses and protractors Hi, Heather. This is not exactly a math question, but I like to talk about words too! The word "compass" means "to go around, encircle"; it originally meant "to measure" by pacing (passus). Since a compass "goes around," this makes some sense. "Protract" originally meant "to drag out, lengthen." How is that related to what a protractor does? My dictionary gives one definition as "[surveying] To draw to scale by means of a scale and protractor." I suspect that because scale drawings or maps make heavy use of angles (remember the AAA similarity theorem: a scale drawing is similar to the original), the protractor was originally thought of as a tool for protracting in this sense. Words don't have to make sense to be used, but I think we can see at least a little sense in the history behind these words. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/
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